1. Field of the Invention
The present invention relates to extracting the base metals copper, nickel, cobalt or zinc from materials containing them.
2. Description of the Related Art
Copper sulphide concentrates are typically processed to metal by smelters. Although very efficient, smelters generate substantial quantities of sulphur dioxide gases (SO.sub.2) that must be captured to protect the environment. The SO.sub.2 captured is normally converted to sulphuric acid. The capture of SO.sub.2 and the generation of sulphuric acid significantly increase the costs of smelting copper sulphide concentrates and generates a by-product, sulphuric acid, that has a very weak market because of surplus and transportation costs.
Some gold ores or concentrates containing cyanide-soluble copper minerals cannot be treated economically because of the high operating costs due to the consumption of cyanide by copper.
Various hydro-metallurgical processes have been developed to replace smelters for treating copper sulphide concentrates. Among others, these processes include pressure leaching (either at high, medium or low temperature), ferric ion (Fe.sup.3+) leaching, and bacterial leaching.
The ability of ferric ion to attack metal sulphides is generally known. In the case of Chalcopyrite (CuFeS.sub.2), Coveilite (Cu.sub.2 S), or Chalcocite (CuS) concentrates, the oxidation/leaching reactions with ferric can be written as: EQU CuFeS.sub.2 +4Fe.sup.3+.fwdarw.Cu.sup.2+ +5Fe.sup.2+ +2S.sup.0 (1)
Cu.sub.2 S+4Fe.sup.3+.fwdarw.2Cu.sup.2+ +4Fe.sup.2+ +S.sup.0 (2) EQU CuS+2Fe.sup.3+.fwdarw.Cu.sup.2+ +2Fe.sup.2+ +2S.sub.0 (3)
The ferric can be added either as ferric chloride or ferric sulphate, although it is known that ferric chloride is kinctically favored over ferric sulphate.
Reactions (1) and (2) indicate that, for example, to dissolve 20 g/L Cu in solution, the leach solution needs at least 70 g/L Fe.sup.3+ and 17.4 g/L Fe.sup.3+ for Chalcopyrite and Covellite concentrates respectively. Though useful as a replacement for smelters, ferric ion reaction processes are undesirable, in some cases, because they generate leach solutions containing high levels of dissolved salts and are difficult to process further. Chalcopyrite is known to be a copper mineral which is refractory to chemical dissolution in typical leach conditions, and the reaction (1) indicates that it requires a relatively high dosage of ferric to be dissolved in acid solutions.
One alternative is to regenerate the ferric during the leaching process, that is by oxidizing the ferrous ion to its ferric state. Conventionally either chlorine gas or pure oxygen are used as oxidants in this case, the former in the following reaction: EQU FeCl.sub.2 +1/2Cl.sub.2.fwdarw.FeCl.sub.3 (4)
However, chlorine gas is expensive and relatively dangerous to handle and the reaction using pure oxygen gas is too slow to be a feasible oxidant.
Copper heap leaching has become the method of choice, particularly for treating low grade oxidized copper ores, The method is only partially successful in treating copper ores containing secondary copper minerals such as Chalcocite and Covellite, unless the dissolution of these copper minerals is bacterially assisted by organisms such as Thiobacillus Ferroxidans and Thiobacillus Thiooxidans. The practical application of these bacteria strains is delicate because they require a precise range of temperatures and acidity as well as a range of specific nutrients in order to function properly.
It is an object of the present invention to obviate or mitigate the above mentioned problems.
It is another aspect of the present invention to provide a novel technique for extracting a base metal from a material.
It is still another object of the present invention to provide a novel technique for extracting a base metal from a sulphide material.
It is still another object of the present invention to provide a process by which copper sulphide concentrate can be efficiently leached by ferric sulphate solutions using lower overall ferric ion concentrations than in prior art processes.